The inventive concepts described herein relate to an adjustable capacitor, a plasma impedance matching device, a plasma impedance matching method, and a substrate treating apparatus, and more particularly, relate to an adjustable capacitor capable of adjusting capacitance, a plasma impedance matching device capable of matching plasma impedance in a process apparatus, using plasma, of a semiconductor fabricating equipment, a plasma impedance matching method, and a substrate treating apparatus.
A plasma impedance matching device uses a Radio Frequency (RF) power, and is an impedance matching device for enabling a maximum RF power to be transferred to a plasma process chamber. Thus, the plasma impedance matching device may be a principal device to generate and maintain plasma.
When a power generated by an RF power supply is supplied to a process chamber for generating plasma, impedance of a power supply and plasma impedance must be matched to transfer a maximum power without a reflected wave. This operation is generally called impedance matching.
Plasma impedance being an electric characteristic is varied according to conditions such as pressure, RF power, source gas, and the like. In case that the plasma impedance is not matched with impedance of the RF power supply, it is difficult to supply a power constantly. This causes a variation in a plasma density at processing. As a result, a difference of process results becomes large. For this reason, impedance matching may be considered to transfer the RF power to the process chamber constantly. For this, an impedance matching device is disposed between the RF power supply and a plasma generating device within the process chamber.
A conventional impedance matching device is formed of an adjustable capacitor and an inductor. Impedance of the RF power supply is matched with impedance of the process chamber by adjusting capacitance of the adjustable capacitor.
Capacitance of the adjustable capacitor within the conventional impedance matching device is varied by adjusting an interval of the capacitor using a driving means formed of a stepping motor and a gear stage. Impedance of the RF power supply is varied by adjusting capacitance of the adjustable capacitor.
In case that capacitance of the capacitor is adjusted by a mechanical driving means, a time delay becomes longer by an operating time of the mechanical driving means, and it is difficult to control capacitance finely. In particular, in the event that the RF power supplies a power in a pulse mode, a plasma state is rapidly varied at a high-speed pulse. For this reason, it is difficult to perform impedance matching rapidly. Further, the RF power may be supplied in a pulse mode where an RF power supply voltage becomes periodically on and off according to a time. In this case, although the pulse mode is at an off state, a power remaining at the adjustable capacitor is supplied to the process chamber.